The present invention relates to a method of discriminating a state of an object on a seat (for example, whether or not a human being is on board, whether or not the human being on board is an adult or a child) based on a signal (seat load) from a seat load meter for measuring the weight of the seat and the object placed thereon.
Hitherto, a seat load meter for measuring the weight of a seat and an object which is placed thereon (normally a human being) is often provided under the seat. Such a seat load meter is used, for example, for controlling deployment of an airbag.
In the control of deployment of the airbag, when the object placed on the seat is a child or a child seat, the airbag is controlled to be deployed by a soft-deployment mode. When the seat is vacant, the airbag may be controlled so as not to be deployed.
In this manner, it is necessary to know the state of the object placed on the seat according to the measured value (seat load) measured by the seat load meter. Therefore, generally, a method of discriminating by discriminating several thresholds for the seat load and, for example, discriminating the seat to be vacant when the seat load is a first threshold or below, to be occupied by a child when the seat load is between the first threshold and a second threshold exclusive, to be occupied by an adult when the seat load is between the second threshold and a third threshold, and to be loaded with a child seat when it exceeds the third threshold is employed.
However, in practice, the output of the seat load meter changes with time as a result of change in posture of the human being, the vertical acceleration, etc., during movement of the vehicle. Therefore, when the measured value is close to the threshold, the output of the seat load meter often exceeds the threshold and moves up and down. In such a case, discrimination of the state of the object placed on the seat changes frequently, and hence unfavorable influences may exist.
As a method of preventing such frequent change in discrimination of the state, Japanese Unexamined Patent Application Publication No. 2001-74541 (Patent Document 1), the contents of which are incorporated herein by reference in their entirety, discloses a method of dividing one threshold into two for providing hysteresis for the discrimination of the state.
As a method of preventing frequent change in discrimination of the state, there is a method of discrimination the state to correspond to the range of the seat loads when the ratio of the actual measured value of the seat load being within a predetermined range of the seat loads reaches or exceeds a predetermined value. This method is shown with reference to FIGS. 5(a) and 5(b). In FIGS. 5(a) and 5(b), there are provided three thresholds TH1, TH2, and TH3, whereby the state is divided into class 1 to class 4.
The method of discriminating the state is such that the output of the seat load meter is sampled, and when four data out of five samplings are in the same class, the state is switched to the corresponding class. In FIG. 5(a), at the beginning, since all data exceed TH3, and in Class 4, it is discriminated to be in the state of Class 4. In the next five samplings, since four data are between TH1 and TH2, which corresponds to Class 2, the discriminated state is switched to Class 2. Then, in the next five samplings, since four data are between TH1 and TH2, which corresponds to Class 2, the discriminated state remains in Class 2. In the next five samplings, four data are between TH2 and TH3, which corresponds to Class 3, the discriminated state is switched to Class 3.
However, the method used to discriminate the state when receiving input as shown in FIGS. 5(a) and 5(b) has a problem. For example, as shown in FIG. 5(b), the measured value of the seat load meter may fluctuate around the threshold, and when four samplings are not in the same class as a result of five times of sampling, the previous state is maintained indefinitely, and hence the discriminated state departs from the actual state.
In FIG. 5(b), since all data exceed TH3 at the beginning, the state is discriminated to be Class 4. In the next five samplings, since only three data are in Class 2. Therefore, the state is not discriminated to be Class 2, and the discriminated state is maintained in Class 4. Then, in the next five samplings, since only three data are in Class 1, the state is not discriminated to be Class 1, and the discriminated state is maintained in Class 4. In the next five samplings, since only three data are in Class 2, the state is not discriminated to be Class 2, and the discriminated state is maintained in Class 4. In this manner, the state in which the state is discriminated to be Class 4 continues although the actual data shows Class 1 or Class 2.
In view of such problems, it is an object of the present invention to provide a method of discriminating the state of an object on a seat in which the state can be switched to the state that can be discriminated accurately even when the measured value fluctuates around the threshold.